A commercially available 99mTc generator is an instrument for extracting the metastable isotope 99mTc from a source which contains decaying 99Mo.
99Mo in turn is usually obtained from a method which uses highly enriched uranium 235U as a target. 99Mo is created as a fission product by irradiating the target with neutrons. However, as a result of international treaties, it will become ever more difficult in future to operate reactors with highly enriched uranium, which could lead to shortages in the supply of radionuclides for SPECT imaging.